Field of the Invention
The present invention relates to a thin film transistor array and a manufacturing method of the same.
Discussion of the Background
Due to the remarkable development of information technology, nowadays, information is frequently transmitted and received with laptop computers or portable information terminals. It is common knowledge that a ubiquitous society enabling information to be exchanged anywhere will be attained in the near future. In such a society, a lighter and slim information terminal is desired.
Currently, silicon-based materials are mainly employed as semiconductor materials, and photolithography is generally used as a manufacturing method.
In recent years, printable electronics in which an electrical component is manufactured by using a printing technique are attracting attention. By using the printing technique, the following advantages can be attained, that is, equipment cost and manufacturing cost are reduced compared to using the photolithography and, since a vacuum and high temperature environment are not necessary, a plastic substrate can be used. The printing process efficiently utilizes materials and involves neither a developing process nor an etching process, producing a smaller amount of liquid waste. Accordingly, the environmental load caused by use of printing methods is small.
However, use of printing methods is likely to bring about low pattern definition and low alignment accuracy compared to the photolithography. In particular, in the case where a thick film having a thickness on the order of several micrometers is required, screen printing is often used. However, in this case, a high definition pattern is difficult to be formed from the view point of the fluidity of the paste.
It has been known that the thin film transistors change their semiconductor characteristics, when irradiated with light. Hence, it is considered that light shielding layers should be provided. However, in the case where a light shielding layer is formed by using a printing method, if a high resolution pattern cannot be formed or high alignment accuracy cannot be achieved, the light shielding properties are insufficient. As a result, the thin film transistor may not operate properly.
As a printing method having a resolution higher than that of screen printing, gravure offset printing can be used (e.g., PTL 1). In gravure offset printing, a pattern is formed via a silicone blanket. When the paste is transferred onto the silicone blanket from an intaglio, solvent is absorbed by the blanket to lower the fluidity. As a result, the resolution is improved.
However, in the case where a pattern-formed region is wider than a non-pattern-formed region such as in an upper pixel electrode pattern, the amount of solvent absorbed by the silicone blanket increases, causing a change in the time taken for lowering the fluidity or causing lowering of the alignment accuracy due to swelling of the blanket.
PTL 1: JP-A-2011-37999